The purpose of the work remains a study of Fetal Growth and Development specifically the mechanisms whereby the fetus acquires the metabolic substrates necessary for this process. Particular attention will be paid to the regulation of the uterine blood flow, particularly the role of hormones released by the trophoblast. Studies will be carried out primarily on sheep. Correlations will be sought between rates of uterine blood flow and oxygen consumption and concentrations and rates of release of estrone, estradiol and progestins by the trophoblast.